Implantable stimulation devices deliver electrical stimuli to nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and Deep Brain Stimulators (DBS) to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability with any Implantable Medical Device (IPG) or in any IPG system, such as in a Deep Brain Stimulation (DBS) system as disclosed in U.S. Pat. No. 9,119,964.
An SCS system typically includes an Implantable Pulse Generator (IPG) 10 shown in plan and cross-sectional views in FIGS. 1A and 1B. The IPG 10 includes a biocompatible device case 30 is configured for implantation in a patient's tissue that holds the circuitry and battery 36 (FIG. 1B) necessary for the IPG to function. The IPG 10 is coupled to electrodes 16 via one or more electrode leads 14 that form an electrode array 12. The electrodes 16 are configured to contact a patient's tissue and are carried on a flexible body 18, which also houses the individual lead wires 20 coupled to each electrode 16. The lead wires 20 are also coupled to proximal contacts 22, which are insertable into lead connectors 24 fixed in a header 28 on the IPG 10, which header can comprise an epoxy for example. Once inserted, the proximal contacts 22 connect to header contacts 26 in the lead connectors 24, which are in turn coupled by electrode feedthrough pins 34 through an electrode feedthrough 32 to circuitry within the case 30 (connection not shown).
In the illustrated IPG 10, there are thirty-two lead electrodes (E1-E32) split between four leads 14, with the header 28 containing a 2×2 array of lead connectors 24 to receive the leads' proximal ends. However, the number of leads and electrodes in an IPG is application specific and therefore can vary. In a SCS application, the electrode leads 14 are typically implanted proximate to the dura in a patient's spinal cord, and when a four-lead IPG 10 is used, these leads can be split with two on each of the right and left sides. The proximal contacts 22 are tunneled through the patient's tissue to a distant location such as the buttocks where the IPG case 30 is implanted, at which point they are coupled to the lead connectors 24. As also shown in FIG. 1A, one or more flat paddle leads 15 can also be used with IPG 10, and in the example shown thirty two electrodes 16 are positioned on one of the generally flat surfaces of the head 17 of the paddle lead, which surface would face the dura when implanted. In other IPG examples designed for implantation directly at a site requiring stimulation, the IPG can be lead-less, having electrodes 16 instead carried by the case of the IPG for contacting the patient's tissue.
As shown in the cross section of FIG. 1B, the IPG 10 includes a printed circuit board (PCB) 40. Electrically coupled to the PCB 40 are the battery 36, which in this example is rechargeable; other circuitry 46 coupled to top and/or bottom surfaces of the PCB 40, including a microcontroller or other control circuitry necessary for IPG operation; a telemetry antenna—42a and/or 42b—for wirelessly communicating data with an external controller 50 (FIG. 2); a charging coil 44 for wirelessly receiving a magnetic charging field from an external charger (not shown) for recharging the battery 36; and the electrode feedthrough pins 34 (connection to circuitry not shown). If battery 36 is permanent and not rechargeable, charging coil 44 would be unnecessary.
Either or both of telemetry antennas 42a and 42b can be used to transcutaneously communicate data through the patient's tissue to an external device such as the external controller 50 shown in FIG. 2. Antennas 42a and 42b are different in shape and in the electromagnetic fields they employ. Telemetry antenna 42a comprises a coil, which can bi-directionally communicate with an external device via a magnetic induction communication link, which comprises a magnetic field of typically less than 10 MHz operable in its near-field to communicate at a distance of 12 inches or less for example. Telemetry antenna 42b comprises a short-range Radio-Frequency (RF) antenna that operates in accordance with a short-range RF communication standard and its underlying modulation scheme and protocol to bi-directionally communicate with an external device along a short-range RF communication link. Short-range RF communication link typically operates using far-field electromagnetic waves ranging from 10 MHz to 10 GHz or so, and allows communications between devices at distances of about 50 feet or less. Short-range RF standards operable with antenna 42b include, for example, Bluetooth, BLE, NFC, Zigbee, WiFi (802.11x), and the Medical Implant Communication Service (MICS) or the Medical Device Radiocommunications Service (MDRS). Short-range RF antenna 42b can take any number of well-known forms for an electromagnetic antenna, such as patches, slots, wires, etc., and can operate as a dipole or a monopole. IPG 10 could contain both the coil antenna 42a and the short-range RF antenna 42b to broaden the types of external devices with which the IPG 10 can communicate, although IPG 10 may also include only one of antenna 42a and 42b. 
Implantation of IPG 10 in a patient is normally a multi-step process, as explained with reference to FIG. 3. A first step involves implantation of the distal ends of the lead(s) 14 or 15 with the electrodes 16 into the spinal column 60 of the patient through a temporary incision 62 in the patient's tissue 5. (Only two leads 14 with sixteen total electrodes 16 are shown in FIG. 3 for simplicity). The proximal ends of the leads 14 or 15 including the proximal contacts 22 extend externally from the incision 62 (i.e., outside the patient), and are ultimately connected to an External Trial Stimulator (ETS) 70. The ETS 70 is used during a trial stimulation phase to provide stimulation to the patient, which may last for two or so weeks for example. To facilitate the connection between the leads 14 or 15 and the ETS 70, ETS extender cables 80 may be used that include receptacles 82 (similar to the lead connectors 24 in the IPG 10) for receiving the proximal contacts 22 of leads 14 or 15, and connectors 84 for meeting with ports 72 on the ETS 70, thus allowing the ETS 70 to communicate with each electrode 16 individually. Once connected to the leads 14 or 15, the ETS 70 can then be affixed to the patient in a convenient fashion for the duration of the trial stimulation phase, such as by placing the ETS 70 into a belt worn by the patient (not shown). ETS 70 includes a housing 73 for its control circuitry, antenna, etc., which housing 73 is not configured for implantation in a patient's tissue.
The ETS 70 essentially mimics operation of the IPG 10 to provide stimulation to the implanted electrodes 16, and thus includes contains a battery within its housing along with stimulation and communication circuitry similar to that provided in the IPG 10. Thus, the ETS 70 allows the effectiveness of stimulation therapy to be verified for the patient, such as whether therapy has alleviated the patient's symptoms (e.g., pain). Trial stimulation using the ETS 70 further allows for the determination of particular stimulation program(s) that seems promising for the patient to use once the IPG 10 is later implanted into the patient. A stimulation program may specify for example which of the electrodes 16 are to be active and used to issue stimulation pulses; whether those active electrodes are to act as anodes or cathodes; the current or voltage amplitude (A) of the stimulation pulses; the pulse width (PW) of the stimulation pulses; and frequency (f) of the stimulation pulses, as well as other parameters.
The clinician programmer system of FIG. 3 can also be used generally by a clinician to communicate with and program the IPG 10 once it is fully implanted in a patient. Such communication again would occur via communication link 92. Thus the clinician programmer system may be used during patient check-ups for example to update the stimulation program the IPG 10 is running.
An example of stimulation pulses as prescribed by a particular stimulation program is illustrated in FIG. 4. As shown, and as is typical in an IPG, each stimulation pulse is biphasic, meaning it comprises a first pulse phase followed essentially immediately thereafter by an opposite polarity pulse phase. The pulse width (PW) could comprise the duration of either of the pulse phases individually as shown, or could comprise the entire duration of the biphasic pulse including both pulse phases.
Biphasic pulses are useful because the second pulse phase can actively recover any charge build up after the first pulse phase residing on capacitances (such as the DC-blocking capacitors 107 discussed later with respect to FIG. 7) in the current paths between the active electrodes. In the example stimulation program shown, electrode E4 is selected as the anode electrode while electrode E5 is selected as the cathode electrode. The pulses as shown comprise pulses of constant current, and notice that the amplitude of the current at any point in time is equal but opposite such that current injected into the patient's tissue by one electrode (e.g., E4) is removed from the tissue by the other electrode (E5). Notice also that the area of the first and second pulses phases are equal, ensuring active charge recovery of the same amount of charge during each pulse phase. Although not shown, more than two electrodes can be active at any given time. For example, electrode E4 could comprise an anode providing a +10 mA current pulse amplitude, while electrodes E3 and E5 could both comprise cathodes with −7 mA and −3 mA current pulse amplitudes respectively.
Referring again to FIG. 3, the stimulation program executed by the ETS 70 can be provided or adjusted via a wired or wireless link 92 (wireless shown) from a clinician programmer 90. As shown, the clinician programmer 90 comprises a computer-type device, and may communicate wirelessly with the ETS 70 via link 92, which link may comprise magnetic inductive or short-range RF telemetry schemes as already described. Should the clinician programmer 90 lack a communication antenna, a communication head or wand 94 may be wired to the computer which has a communication antenna. Thus, the ETS 70 and the clinician's programmer 90 and/or its communication head 94 may include antennas compliant with the telemetry scheme chosen. Clinician programmer 90 may be as described in U.S. Patent Application Publication 2015/0360038. External controller 50 (FIG. 2) may also communicate with the ETS 70 to allow the patient means for providing or adjusting the ETS 70's stimulation program.
At the end of the trial stimulation phase, a decision is made whether to abandon stimulation therapy, or whether to provide the patient with a permanent IPG 10 such as that shown in FIGS. 1A and 1B. Should it be determined that stimulation therapy is not working for the patient, the leads 14 or 15 can be explanted from the patient's spinal column 60 and incision 62 closed in a further surgical procedure.
By contrast, if stimulation therapy is effective, IPG 10 can be permanently implanted in the patient as discussed above. (“Permanent” in this context generally refers to the useful life of the IPG 10, which may be from a few years to a few decades, at which time the IPG 10 would need to be explanted and a new IPG 10 implanted). Thus, the IPG 10 would be implanted in the correct location (e.g., the buttocks) and connected to the leads 14 or 15, and then temporary incision 62 can be closed and the ETS 70 dispensed with. The result is fully-implanted stimulation therapy solution. If a particular stimulation program(s) had been determined during the trial stimulation phase, it/they can then be programmed into the IPG 10, and thereafter modified wirelessly, using either the external programmer 50 or the clinician programmer 90.